netdev - RE: [PATCH net-next RFC 0/5] Add NTF_EXT_AGED to control FDB ageing in SW or HW

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Message-ID: <FFEDCF9956066D4D97C463CC178C7F69F22E02@SJEXCHMB06.corp.ad.broadcom.com>
Date:	Sat, 21 Feb 2015 00:20:23 +0000
From:	Viswanath Bandaru <vbandaru@...adcom.com>
To:	Florian Fainelli <f.fainelli@...il.com>,
	roopa <roopa@...ulusnetworks.com>,
	"sfeldma@...il.com" <sfeldma@...il.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"jiri@...nulli.us" <jiri@...nulli.us>,
	"linux@...ck-us.net" <linux@...ck-us.net>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"gospo@...ulusnetworks.com" <gospo@...ulusnetworks.com>,
	"siva.mannem.lnx@...il.com" <siva.mannem.lnx@...il.com>
Subject: RE: [PATCH net-next RFC 0/5] Add NTF_EXT_AGED to control FDB ageing
 in SW or HW


> -----Original Message-----
> From: Florian Fainelli [mailto:f.fainelli@...il.com]
> Sent: Saturday, February 21, 2015 12:44 AM
> To: roopa; sfeldma@...il.com
> Cc: netdev@...r.kernel.org; jiri@...nulli.us; linux@...ck-us.net;
> andrew@...n.ch; gospo@...ulusnetworks.com; Viswanath Bandaru;
> siva.mannem.lnx@...il.com
> Subject: Re: [PATCH net-next RFC 0/5] Add NTF_EXT_AGED to control FDB
> ageing in SW or HW
> 
> On 20/02/15 09:29, roopa wrote:
> > On 2/19/15, 11:09 PM, sfeldma@...il.com wrote:
> >> From: Scott Feldman <sfeldma@...il.com>
> >>
> >> Add a new NTF_EXT_FLAG to mark an FDB as externally aged, for example
> by
> >> offload hardware.   Switchdev driver/devices can set this flag when
> >> learning a
> >> new FDB entry and SW (the bridge driver) will skip this entry when
> >> running its ageing task.  If flag is set, the driver/device is
> >> responsible for calling
> >> call_netdev_switch_notifiers(NETDEV_SWITCH_FDB_DEL, ...) when entry
> >> expires.
> >>
> >> This give the flexibility for driver/device to decide ageing policy
> >> based on its capabilities.  For devices managing many FDB entries, it
> >> is desireable for the device to aged out its own entries.  Devices
> >> not capable of aged entries can rely of SW to age out the entries.
> >>
> > scott, patches look good. However, I am not sure yet if there is a
> > need to make it a per fdb entry flag.
> 
> I agree, in fact, most of the HW I have access to only has a global age timer
> configuration knob. Is this configurable on a per-port basis for higher end
> switches, or even maybe per-FDB entry?
> 

The decision to age an entry is on a per-FDB entry, So if the flag is not available in the fdb-entry, then it has to be obtained from associated netdev. I think the per-FDB may be more convenient than keeping it on netdev. 

> >
> > At some point we will also need the hw ageing parameter to be
> configurable.
> > So other approach could be,
> > - ageing parameter on bridge gets offloaded the hw

Like everybody said, the ageing is really the switch's property.  If there are two bridges with ports from same switching device, it becomes tricky to configure ageing time on the switch.  ( I think this is what you may be referring to be saying it needs more thought).

> > - so, by default hw and kernel age their own entries using the same
> > bridge device default timer
> > - User can explicitly disable HW ageing by using self (this needs some
> > more thought because now the call is on the bridge device)
> 
> I think we want to be careful with both SW and HW aging entries since a host
> CPU's clock might be suspended/drifting etc.. at least, we probably want one
> or the other to take precedence other the other one?
> --
> Florian